Ian, I am glad your arranger does just what you want it to do. My G70 does what I want it to do...

I just don't ask it to do EVERYTHING

Thing is, I guess it depends at what level you are recording at. My label clients expect a better overall sound than any arranger can get by itself (otherwise I'd be only too happy to use the one thing!). Yes, I've used my G70 on quite a few projects, but I've also HAD to use other things, the Kurzweil, Tritons, Nord's, REAL B3 and Steinway, many VSTi's, whatever I need to record with.
SOME things in the G70 are good enough, some aren't. There's a lot to like about the S910, but I'm pretty sure that, for my use, I'd have to say the same thing for it, too...